Currently, more than 2.8 million breast cancer survivors are living in the United States. While breast cancer survival has dramatically increased over the last few decades, the risk and fear of developing lymphedema (LE) after axillary surgery for breast cancer remains a source of significant anxiety for these women and has been documented to adversely affect survivorship and quality of life. Thus, key issues in the field center on improving our understanding of the underlying mechanisms that promote post-surgical LE, enhancing our ability to accurately predict which women are at greater risk of LE and identifying molecular targets for the development of novel interventions that could reduce the incidence of LE following breast cancer surgery. The pathogenesis of LE is multi-factorial and is likely determined by anatomical structure, molecular factors, and genetic predispositions to lymphangiogenesis. We hypothesize that LE after axillary surgery is dependent upon both clinical and inherent biological or genetic factors of the individual patient that directly regulat lymphangiogenesis and may be modified by alterations in MMP-9/TIMP-1 and the VEGF-C / VEGFR3 systems, which are known to be key drivers of lymphatic repair in preclinical models. Further, we suggest these changes to tissue repair can be measured in the postoperative lymphatic fluid routinely drained from the axilla after axillary node dissection. In addition, we wll explore the genetic susceptibility to LE by identifying known LE DNA variants in unaffected but high-risk women. We will then investigate if these variants are useful for determination of future LE risk or can be used to stratify women at increased risk for LE for the purpose of prevention or treatment strategies. We propose that these biomarkers of lymphangiogenesis promoting or inhibiting creation of collateral lymphatic vessels maintaining lymphatic flow can be measured and predicted. The overall, long-term goal of our research program is to develop a risk assessment model incorporating clinical, biologic, and genetic factors for a personalized approach to prevention and treatment of LE among patients undergoing axillary surgery for breast cancer. Motivated by this, we will use well annotated biospecimens of lymphatic fluid and fasting blood samples from our Mayo Axillary Surgery Registry, which was initiated by Dr. McLaughlin in 2008 and prospectively captures clinical, follow-up, and quality of life data as well as the valuable biospecimens from surgically-treated breast cancer patients undergoing either axillary surgery at our institution. In this application we will harness this unique resource to evaluate specific aims designed to explore the biologic factors in lymphatic fluid regulating lymphatic tissue repair and lymphangiogenesis, examine the frequency and biological role of germline DNA alterations and examine associations with the development of LE. The efforts described in this application will provide the preliminary data for future R01 funding for the development and validation of a novel LE risk prediction model that incorporates clinical, lifestyle, biologic, and genetic risk factors.